1. Field of the Invention
The invention relates generally to the field of photography, and in particular to a film cassette containing roll film coiled about a spool. More specifically, the invention relates to a film cassette that is capable of automatically advancing a non-protruding film leader through a passageway out of the cassette shell responsive to unwinding rotation of the spool.
2. Description of the Prior Art
Prior art commonly assigned U.S. Pat. No. 5,046,680, filed Mar. 8, 1990 and issued Sept. 10, 1991, discloses a film cassette wherein a spool is supported for rotation in an unwinding direction inside a cassette shell, a filmstrip is coiled about the spool to form a film roll with an outermost convolution having a leading end, a pair of flanges are coaxially arranged along the spool with respective peripheral annular lips or skirts overlapping the outermost convolution adjacent opposite longitudinal edges of the outermost convolution to radially confine the film roll, respective notches are cut in the longitudinal edges at individual locations nearby the leading end which receive sections of the annular lips to allow sections of the longitudinal edges between the notches and the leading end to overlap the annular lips to hold the leading end spaced from a next-inward convolution of the film roll, and a stripper is positioned closer to one of the longitudinal edges than to the other for receipt between the leading end and the next-inward convolution to divert the leading end into a passageway out of the shell when the spool is rotated in the unwinding direction. If the section of the longitudinal edge that is closer to the stripper is allowed to slip from overlapping the annular lip to behind (inside) the annular lip, the stripper may not fit between the leading end and the next-inward convolution to divert the leading end into the passageway when the spool is rotated in the unwinding direction. Instead, the leading end would be advanced underneath the stripper and could not enter the passageway. This problem may occur with the film cassette disclosed in U.S. Pat. No. 5,046,680 because the outermost convolution can be laterally shifted to separate the section of the annular lip in the notch in the longitudinal edge that is closer to the stripper from that notch.
Prior art commonly assigned U.S. Pat. No. 4,883,236, filed Mar. 8, 1989 and issued Nov. 28, 1989, discloses a film cassette somewhat similar to the film cassette disclosed in U.S Pat. No. 5,046,680. In this instance, however, a compression spring is provided to urge the section of the annular lip in the notch that is closer to the stripper into that notch to prevent the section from separating from the notch (as in U.S. Pat. No. 5,046,680).